But an acre of land in the suburbs costs hundreds of thousands or millions of dollars, whereas an acre of land in a normal agricultural area far from a city costs a few thousand dollars.
maybe there has to be a certain chunk of land set aside in urban areas for green and open spaces? concentrating massive food production centers is a terrible idea. not just because its an easy target for bio hacking but also because of the impact on environment and water especially. small distributed food production centers makes much more sense.
In the US, 40% of all its land is in active agriculture production. Most of the remaining 60% is not in production because it is not productive. I suggest production has already spread to everywhere that is viable to do so.
Even if you can find and allocate several thousand acres of productive farmland in every city for growing food, what are you really accomplishing? That's but a tiny little drop in the bucket of all the land needed to sustain the population. Not to mention that many cities rose out of agrarian pasts, so it is quite likely that active farmland is already found on the outskirts.